ABSTRACT
This paper aims to highlight the use of different heat transfer fluid (HTF) configurations based on vegetable oils in Parabolic Trough Solar Concentrator (PTSC). Rapeseed and jatropha oils as innovative heat transfer materials combined with SiO2 and Al2O3 to obtain six (6) HTF configurations are used in a 1-dimensional PTSC model. The thermophysical properties of the nanofluids are determined from correlations derived from the literature, using Gauss-Seidel method from a numerical code developed in Matlab software. Model validation is obtained. Thermal sensitivity analysis shows that the use of rapeseed increases the thermal efficiency of the PTSC by around 4.21 % compared with jatropha. The use of nanofluids reduces thermal losses within the system due to thermal gradients. For a fixed irradiance and each 1 %-4 % increase in volume fraction, thermal efficiency increases by around 1.96 % when Al2O3/rapeseed is used and by 0.47 % when SiO2/rapeseed is used compared with rapeseed. Similarly, thermal efficiency increases by around 1.98 % when Al2O3/jatropha is used and decreases by around 0.20 % when SiO2/jatropha is used compared with jatropha. However, the positive effects of nanoparticles on thermal conductivity alone are not always sufficient to improve thermal efficiency, and thermal effects on heat capacity should also be considered.
ABSTRACT
Access to reliable energy is fundamental for the development of any community. The electricity is produced in Chad solely from thermal plants that use fossil fuels, which are not environmentally friendly. In addition, the electrification rate of Chad is less than 11%. This work aims to propose some reliable electrification options for Chad, through hybrid energy systems. To achieve this objective, autonomous hybrid PV/Diesel/Wind/Batteries feasibility to meet the demand of electrical load in isolated regions of Chad is evaluated using HOMER software. The design is done considering three types of daily load profiles in each of the 16 regions that are not yet electrified in Chad; the low, medium and high community load profiles. From the simulation, it was observed that the optimal configurations were: PV/Battery, PV/Diesel/Battery and PV/Wind/Diesel/Battery for various consumers and sites. The COE was found to be in the range of 0.367 and 0.529 US$/kWh which shows that, the COE of some sites are less than the production cost of energy in Chad (0.400 US$/kWh) and therefore profitable. Using these hybrid systems, compared to single diesel generator will result in less CO2 emission per year (between 0 and 15670 kg/year). These results may guide investors and policies makers in the planning and implementation of various optimal feasible options that may be used to increase the electricity access rate of Chad, especially in remote areas.
ABSTRACT
Nowadays ferrofluids (magnetic nanofluids) are at the center of many researches because of their major biomedical applications such as drug delivery and cancer treatment. The effects of chemical reaction, temperature gradient induced mass transfer and concentration gradient induced heat transfer on the stability of ferrofluid flow are of great importance. This paper deals with a stability analysis of a ferrofluid composed of blood as base fluid and magnetic nanoparticles. The study integrates the effects of chemical reactions, the effects of mass transfer (Soret effect), the effects of heat transfer (Dufour effect) and the effects of the Buoyancy force. The flow is exposed to a magnetic field and thermal radiation. A system of eigenvalue equations governing the evolution of disturbances is derived by assuming a normal mode analysis. This system of equations is then solved numerically by the method of collocation. It appears from this study that the addition of nanoparticles to the blood increases its inertia, which dampens the amplitude of the disturbances and stabilizes the flow. The Casson parameter affects the stability of the flow by increasing the amplitude of the disturbances, which reflects its destabilizing effect. It appears from this study that taking into account the non-Newtonian nature of blood is very important when modeling the dynamics of the system because it shows more important and very different results than when blood is treated as a Newtonian fluid. The chemical reaction between the fluid and the nanoparticles leads to the redistribution of disturbances within the flow, which amplifies the instabilities and reflects the destabilizing character of the chemical reaction. On the other hand, temperature gradient induced mass transfer effects and concentration gradient induced heat transfer effects play an essential role on the stability of the flow because they attenuate the amplitude of the disturbances in the flow. The Darcy number exhibits a stabilizing effect on the flow. It appears from this analysis that the porosity of the medium increases the contact surface between the fluid and the nanoparticles. Buoyancy forces, thermal radiation parameter and wave number contribute to the stability of the flow. The magnetic field through the Lorentz force decreases the kinetic energy of the flow, which dissipates the disturbances and thus reflects the stabilizing character of the magnetic field. It should be noted that heat and mass transfer on magnetohydrodynamic flows through porous media taking into consideration the effect of chemical reaction appears in many natural and artificial transport processes in several branches of science and engineering applications. This phenomenon plays an important role in the chemical industry, power and cooling industry for drying, chemical vapor deposition on surfaces, cooling of nuclear reactors and petroleum industry. The effects of thermal radiation, mass and heat transfer are used in many situations in biomedical engineering and aerospace engineering.
ABSTRACT
The propagation of radiation in an absorbing-scattering soil with constant or spatial variation of the refractive index is investigated. The soil consists of a plane parallel with Fresnel reflection at the boundaries and is exposed at one boundary to a diffuse or collimated incident radiation. The discrete spherical harmonics method using Marshak boundary conditions is introduced to approximate the directional hemispherical reflectance and transmittance as well as the bidirectional reflectance. The effect in spatial variation of the refractive index on the reflectance and transmittance predictions is examined. A comparison of the directional transmittance and reflectance with the literature results demonstrates that the present method gives accurate results for optically thin and thick soil with a maximum relative error in all cases less than 1%. The bidirectional radiance for variable refractive index soils also shows excellent agreement as compared to the literature results. The results demonstrated that the anisotropic soil interfaces cause a significant decrease of energy reflected and transmitted as well as the bidirectional reflectance.
